Droughts destroying Earth’s biggest carbon sink on land: study

By Mark Waghorn via SWNS

Droughts are destroying Earth's biggest carbon sink on land, according to new research.

Soil stores more greenhouse gas than plants and the atmosphere combined - thanks to the microbes that live in it.

Moisture plays a key role in the process. Lack of rainfall is disrupting this delicate ecosystem.

Lead author Dr. Steven Allison, of California University of Irvine, said: "Soil microbes are beneficial and we couldn't live without their cycling of carbon and nutrients.

"But climate change and drought can tweak that balance - and we have to be aware of how it's changing."

There's about six times more carbon in soil than there is in the plants that grow on it. Only the oceans contain more.

Global warming is causing water shortages across the globe.

Last summer Northern Italy had its worst drought in 70 years. Almost half US states had them. Summer 2022 in the UK was the driest since 1995 - and the second hottest on record.

The UN says drought frequency and duration has increased by nearly a third since 2000.

Some soil microbes take carbon from decomposing plants and store it in the soil, while others release plant carbon back into the atmosphere.

The carbon that ends up in the soil is beneficial in multiple ways.

Allison said: "The carbon in the soil has these reverberating effects out to the rest of the world in terms of the infrastructure in our natural and managed ecosystems.

"Carbon-rich soils hold more nutrients, so plants growing in those soils tend to be more productive, and the carbon changes the physical properties of the soil, which prevents erosion.

“In California now, we have this system where the droughts are more intense, and then the rainfall is more intense.

"So, if you're losing your soil carbon, when it rains really hard it could carry away your soil and cause erosion, landslides, mudslides, sediments, and all kinds of problems we're actually seeing right now."

The carbon that is released back into the atmosphere is another story.

Dr Allison said: "From a climate mitigation standpoint, what we want is for more carbon to be in plants and soils and less carbon to be in the atmosphere, so the more carbon we can absorb into plants through photosynthesis and the more we can transfer and keep in the soil, the better off we're going to be in terms of climate change.

"That's why it's really important to know how the balance of incoming versus outflowing carbon changes with drought, or warming, or any other climate factor."

Plants and microbes will both be impacted by the increasing frequency of drought. It's hoped microbes will be able to bounce back faster.

Allison said: "Microbes are really adaptable—they can change their physiology, they can change their abundances so that more drought-adapted microbes take over, and they can potentially evolve—so we expect that they are going to resist or bounce back from drought.

"All those different processes can happen pretty quickly with microbes, and much more quickly than with plants."

If more carbon-releasing microbes survive than carbon-sequestering microbes, we could end up with carbon-depleted soils, which would have serious negative implications for plant productivity and future greenhouse gas levels.

We may be able to nudge the balance in the right direction - but more research is needed first, according to the study, published in the journal Trends in Microbiology.

Allison said: "There's still a lot to be done. Right now, we have data that suggests that when we have drought, something changes that results in carbon loss, but we don't understand exactly how or why that's happening, whether drought’s changing the abundance of beneficial plant associated microbes versus the carbon releasing microbes, or if it's causing the evolution of one of the microbe groups, or if it's more determined by changes to their immediate physiology."

Some microbes could actually help plants cope with drought. If it was known which microbes were most beneficial to plants, and most likely to retain carbon in soil, then we could try to tip the balance in their favor.

Allison said: "There's a lot of potential for us to manage or engineer soil microbes.

"In agricultural systems, we can look into manipulating the soil or adding beneficial microbes back in.

"In more natural systems, management would probably be on the plant side: soil microbes are often closely intertwined with plants, so managing the plants can also benefit the microbial part of the ecosystem.

"We also need more measurements to get a good sense of how drought affects soil carbon change in different ecosystems.

"There's a lot of landscape out there—from the Arctic tundra to the deserts—and we could use more research across those diverse habitats."